(1) Field of the Invention
The present invention relates to amorphous silica-alumina spherical particles having a novel particulate form and characteristics desirable for a filler or pigment, and a process for the preparation thereof.
(2) Description of the Prior Art
Amorphous silica or alumina spherical particles are widely used as a filler for various polymer films and other resins and rubbers, a filler for cosmetics, a supporting carrier for perfumes and chemicals, a filler for the chromatography, and the like.
As the means for producing such silica-alumina spherical particles, processes are known in which a silica-alumina is sprayed and, according to need, the sprayed sol is caused to impinge against an air current, a process in which an organic metal compound is hydrolyzed, and a process in which a crystalline zeolite having a cubic or spherical particulate form is neutralized under such conditions that the crystal structure is substantially destroyed but the particulate form is not substantially destroyed, to remove the alkali metal component from the zeolite.
The silica-alumina spherical particles prepared according to the former process are disadvantageous in that the primary particle size is relatively coarse and the particle size distribution is broad.
For example, when these spherical particles are used as a filler for a resin, a problem arises with respect to the dispersibility in the resin or the compatibility therewith. Namely, if the resin having these silica-alumina spherical particles incorporated therein is formed into a film and the film is drawn, voids (vacant spaces) are readily formed between the resin and the filler particles.
The last-mentioned process is very valuable as the process for the production of amorphous silica particles, but since the alumina component in the zeolite is considerably removed together with the soda component during acid treatment, the alumina component is lost and the particles are structurally changed, and the refractive index of the particles is drastically changed. Therefore, the process is not desirable as the process for the preparation of amorphous silica-alumina particles.
The fatal defect of the conventional silica-alumina spherical particles is that the spherical particles still retain the characteristics of the amorphous silica-alumina adsorbent. Accordingly, if the known silica-alumina spherical particles are incorporated into a resin, blowing is caused when the resulting composition is heat-shaped.